A known transfer system transfers substrates, such as semiconductor wafers, using a robot hand (hereinafter referred to as a “hand”) disposed at a distal end portion of an arm of a multi-axis robot to hold the substrates.
Such a transfer system is used in, for example, semiconductor fabricating processes for transferring substrates to and from various types of process equipment applied, for example, to cleaning, deposition, and photolithography processes (see, for example, Japanese Patent Application Laid-open No. 2008-28134).
It is noted that the substrates are exposed to, for example, a high temperature heating or excessive cooling environment and are very often placed under abnormal temperature as well as normal temperature conditions. In consideration of an adverse effect from the abnormal temperature, the method of holding the substrate may be changed over: specifically, a type of hand that holds or grips the substrate is used for substrates under normal temperature and another type of hand on which the substrate is placed is used for substrates under abnormal temperature.
In conventional transfer systems, however, sufficient consideration has not been given to a traveling speed of the hand to be varied according to the substrate holding method. For example, if the type of hand on which the substrate is placed is used, the substrate is held on the hand mainly through a frictional force. Positional deviation of the substrate may, however, result, if the hand is moved at inordinately high speeds in order to achieve improved throughput.